Rear suspension for bicycles

ABSTRACT

A rear wheel suspension for a bicycle includes paired lower arm members pivotally connected to the bicycle frame seat tube such that they can pivot about an axis situated above the center of the bottom bracket, paired upper arm members adapted to receive the rear wheel axle at hub points located on an axis situated above their lower ends and pivotally connected to the respective lower arm members such that they can pivot about an axis near the rear ends of the lower arm members, and a shock absorber mechanism associated with the upper ends of the upper arm members and pivotally connected to an upper pivot point on the seat tube for limiting the path and the extent of movement of the upper ends of the upper arm members.

This is a continuation of my U.S. patent application, Ser. No.08/303,568, filed Sep. 9, 1994, now U.S. Pat. No. 5,509,679, which is acontinuation of Ser. No. 08/006,325, filed Jan. 21, 1993, now abandoned,which is a continuation-in-part of my U.S. patent application, Ser. No.07/827,089, filed Jan. 21, 1992, now abandoned titled "Rear Suspensionfor Bicycles".

BACKGROUND OF THE INVENTION

i. Technical Field

This invention relates to rear wheel suspensions for bicycles.

ii. Background Art

Conventionally, a bicycle is provided with a frame that is rigid or isflexible only to the extent that particular frame members are flexible.A conventional frame is made of welded generally tubular members,including a generally upright seat tube that supports the seat at itsupper end and abuts the bottom bracket, in which the crank rotates, atits lower end; a generally horizontal top tube that is welded at itsrear end near the top of the seat tube and at its front end to a headtube, in which the front fork, constituting the front wheel suspension,rotates for steering; a down tube that is welded at its upper front endto the head tube and at its lower rear end to the bottom bracket; and arear wheel suspension. The seat tube, top tube, and down tube form therigid generally triangular configuration of the main frame, with thebottom bracket carried at the lower apex. A conventional rigid rearsuspension is made up of a pair of generally horizontal chain stays thatare welded at their front ends to the bottom bracket and are adapted toreceive the rear wheel axle near their rear ends; and a pair of seatstays that are welded at their upper ends near the top of the seat tubeand are welded near the ends of the chain stay arms at their lower ends.The seat tube, chain stays, and seat stays form a rigid generallytriangular configuration, with the rear wheel carried at the rear apex.

Such a conventional rigid arrangement can be suitable for road or trackuse, where the riding surface is generally free of irregularities, butis unsatisfactory for comfort and optimum performance off-road. Ascyclists have demanded higher performance in off-road bicycles,variously referred to as "mountain bikes", "trail bikes", or"cross-country bikes", bicycle makers have recognized the desirabilityof providing a pivoting spring suspension for at least the rear wheel.

Pivoting "swingarm" spring suspensions have long been used for rearwheel suspension on motorcycles. In a simplest configuration, the chainstays are replaced by a pair of arms that are pivotally attached attheir front ends to the frame at a pivot point near the bottom bracket.The rear ends of the swing arms, carrying the rear wheel, move upwardand downward in arcs parallel to the plane described by the rear wheeland centered on the swing arm pivot axis. The range of movement of theswing arms is limited, in a simple configuration, by means such as aspring or a hydraulic shock absorber, affixed between the swing arm anda member of the rigid frame.

Motorcycle frames and swing arms are typically made very heavy, toprovide sufficient strength and rigidity to prevent lateral andtorsional flex. Simple swingarm suspensions have been adapted for use onbicycles in various configurations. In Kamler et al. U.S. Pat. No.5,000,470, for example, a pair of swing arms are pivotally attached tothe main frame at the bottom bracket, and the range of their upward anddownward movement is limited by a pair of shock absorbers that arepivotally attached at their lower ends to pivot points on the swing armsabove the rear wheel axle and at their upper ends to a pivot point onthe seat tube.

When force is applied from the motor or the pedals through the chain tothe rear wheel sprocket, one force component results in forward rotationof the wheel, and another force component tends to urge the wheel axleupward. As a result, in simple swingarm rear suspensions such as aredescribed above, the swing arms pivot sharply upward when a surge ofpower is supplied to the rear wheel, and pivot downward again when thepower is backed off. When a mountain bike, whether motor- orpedal-driven, is worked over rough terrain, this "jacking" can reducethe effective contact of the rear wheel with the riding surface and canseverely compromise the rider's control over the bike.

One proposed remedy for the jacking problem in a motorcycle having asimple swingarm suspension is proposed in McGonegle U.S. Pat. No.4,039,200. McGonegle describes positioning the swing arm pivot axis sothat it intersects the tension run of the drive chain, and preferably sothat it passes through the tangent point of the drive chain tension runwith the power transfer sprocket or the motor drive sprocket.

Jacking further reduces performance because the upward movement of therear wheel results in a dissipation of power that might otherwise go toforward propulsion of the bike. Such losses may be of little consequencefor a motorcycle, but are intolerable to a bicyclist seeking peakperformance.

Where caliper brakes are employed on a bicycle, in a simple swingarmsuspension the caliper is attached to the swing arms. As a result,braking forces are translated to the swing arms, interfering theresponse of the suspension to the riding surface when the brakes areapplied.

Lawwill U.S. Pat. Nos. 4,789,174 and 5,121,937 propose more complexpivoting rear wheel suspensions, in which a pair of swing arms ispivotally attached about or at the bottom bracket; the rear ends of theswing arms are pivotally attached to the lower end of a pair of rear hubplates, which carry the rear wheel; the upper ends of the rear hubplates are pivotally attached to the rear ends of a pair of controlarms; and the front ends of the control arms are attached to a pivotpoint on the seat tube. In Lawwill '937 the swing arms and the controlarms are dimensioned such that the pivot axis at the rear ends of theswing arms is slightly closer to the seat tube than is the pivot axis atthe rear ends of the control arms; this careful maintenance of positionis said to maintain the suspension in careful balance during pedaling,while at the same time permitting absorption irregularities in theriding surface. In Lawwill '174 power losses are said to be neutralizedby virtue of a trapezoid formed by the location of the pivot axestogether with the position of the rear wheel axle. Particularly, thepoint where the control arms pivot on the seat tube is substantiallyabove the rear wheel axle, while the point where the swing arms pivot onthe bottom bracket is only slightly below the rear wheel axle. Thisconfiguration of the swing arms, hub plates, and control arms is said tobalance the forces applied to the rear wheel by the chain duringpedaling so as to prevent energy absorbing movement of the rearsuspension.

SUMMARY OF THE INVENTION

iii. Disclosure of Invention

In one aspect, in general, the invention features a rear wheelsuspension for a bicycle, including paired right and left lower armmembers whose front ends are pivotally connected to the bicycle frameseat tube such that the lower arm members can pivot about a pivot axissituated above the center of the bottom bracket; paired right and leftupper arm members whose lower ends are pivotally connected to therespective lower arm members such that the upper and lower arm memberscan pivot about a pivot axis near the rear ends of the lower armmembers, and adapted to receive the rear wheel axle at hub pointslocated on an axis situated above the horizon of their lower end pivotaxis; and means associated with the upper ends of the upper arm membersand pivotally connected to an upper pivot point on the seat tube forlimiting the path of movement of, and for resiliently limiting theextent of movement of, the upper ends of the upper arm members.

The reader will appreciate that terms of relative position, such as"upper", "lower", "front", "rear", "above", "below", and the like, areused with reference to a bicycle that is standing upright with bothfront and rear wheels resting on a level surface. The "horizon" of apoint, as that term is used here, is an imaginary line made horizontalto the point when the bicycle is standing upright with both front andrear wheels on a level surface.

In another general aspect, the invention features a bicycle having sucha rear suspension.

The bicycle rear wheel suspension according to the invention providesfor isolation of the pedal forces and braking forces from thesuspension, resulting in reduced power dissipation and increasedperformance and improved comfort and safety. The suspension isstructurally resistant to lateral and torsional flex, yet is lightweightand of straightforward construction, and has the traditional appearanceof a bicycle. The suspension according to the invention can be appliedto conventional bicycle main frames, and can accommodate conventionalbicycle components such as standard chain wheels and sprockets,derailleurs, rear wheels, pedals, caliper brakes, and other standardcomponents.

In some embodiments, the means for limiting the path and the extent ofmovement of the upper arm members includes a telescopic shock absorberpivotally connected to the seat tube and rigidly connected to the upperends of the upper arm members. More preferably the means for limitingthe path of movement of the upper end of the upper arm members includesa lever, most preferably an A-arm, which is pivotally connected at oneend to the seat tube end at the other end to the upper end of the upperarm member; and the means for limiting the extent of movement of theupper end of the upper arm member includes a shock absorber operativelyconnected between the lever and the seat tube.

The shock absorber can include a spring or an elastomer or aspring-elastomer combination, or a spring-hydraulic shock absorbercombination.

In preferred embodiments the pivot axis for the front ends of the lowerarm members is situated at a point both above the crank axis horizon andat or below the horizon of the tangent point of a chainwheel with thetension run of the chain; where the bicycle is equipped with two or morechainwheels of different diameter, the pivot axis is preferably situatedat a point at or below the horizon of the tangent point of the smallerone of two chainwheels, or a midsize one of three or more chainwheels,with the tension run of the chain.

DESCRIPTION OF PREFERRED EMBODIMENTS

As will appear in the description following, a person of ordinary skillcan by inspection of the drawings ascertain a full description of theinvention and of how to make and use it. Preferred embodiments are heredescribed, beginning with a brief description of the drawings.

IV. BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram in elevational view showing an embodiment of a rearsuspension according to the invention in operational relation to abicycle, only a part of which is shown in the Figure.

FIG. 2 is a diagram showing the embodiment of FIG. 1 in a rear view.

FIG. 3 is a diagram in elevational view showing an alternativeembodiment of a rear suspension according to the invention inoperational relation to a bicycle, only a part of which is shown in theFigure.

FIG. 4 is a diagram showing the embodiment of FIG. 3 in a rear view.

V. BEST MODE OF CARRYING OUT THE INVENTION

With reference to FIGS. 1 and 2, paired right and left lower arm members2, 102, of which only the right one appears in FIG. 1, are pivotallyattached to seat tube 14 such that they are pivotal about lower armpivot axis 20. Paired right and left upper arm members 3, 103, of whichonly the right one appears in FIG. 1, are pivotally attached torespective right and left lower arm members 2, 102 such that they arepivotal about rear pivot axis 4. The upper ends of upper arm members 3,103 are rigidly connected to one end of telescoping shock absorber 5,and the other end of shock absorber 5 is pivotally attached to seat tube14 at upper pivot point 6. Upper arm members 3, 103 are provided withdropouts 22, 122, of which only the right one appears in FIG. 1, forreceiving rear wheel 12 axle 24 at hub points located on hub axis 26,which is situated to rearward of and above the horizon of rear pivotaxis 4.

Any of a variety of ways, known in the bicycle art, can be employed forestablishing lower arm pivot axis 20 and pivot point 6, for pivotalattachment of the lower arm members 2, 102 and of shock absorber 5.Where the suspension according to the invention is to be retrofittedonto a conventional main frame, brackets provided with holes or pins forpivotal attachment can be clamped onto the seat tube at the appropriatepoints. Where the frame is being manufactured with the suspensionaccording to the invention as original equipment, brackets can be weldeddirectly to the seat tube in the manufacture process.

Preferably, the pivot point 6 is situated at a point opposite the pointof attachment of the top tube, as that provides maximal strength. Therear end of the top tube may interfere with positioning a clamp, andwhere brackets are to be clamped onto the seat tube as a retrofit, theclamp may preferably be positioned immediately below (or lesspreferably, above) the point of attachment of the top tube.

The lower arm member pivot point can be located such that the lower armpivot axis 20 is situated on or above the horizon of the crank axis 28;and the lower arm pivot axis 20 can be situated rearwardly from thecrank axis 28. Typically, as is shown in the Figures, mountain bikes areprovided with two or more chain wheels of various diameters at thecrank, and a cluster of sprockets of various diameters at the rear wheelhub, providing a combination of gearing ratios over a suitably widerange. Where a single chain wheel is provided, the lower arm pivot axisis preferably located at or below the horizon of the tangent point ofthe tension run of the drive chain with the chainwheel, that is, at orbelow the horizon of the point where that chainwheel is first contactedby each link of the chain as the chain runs forward from a rear wheelsprocket to that chainwheel. Generally, where there are two or morechainwheels, the lower arm pivot axis preferably is located at or belowthe horizon of the smaller or smallest chainwheel, as that is the onethat is capable of delivering the greatest forces through the chain tothe rear wheel. Where, owing to the configuration of the bicycle oraccording to the kind of terrain over which it expected to be used, thesmallest of three or more chainwheels would only rarely be employed, itcan be preferable to index the location of the lower arm pivot axis tothe next to smallest one. Thus, where three chainwheels are provided,the lower arm pivot axis 20 is preferably located at or below thehorizon of the tangent point of the tension run 30 of the drive chainwith the midsize one of the three chainwheels, as in the embodimentshown in the Figures, or with the smallest of the three chainwheels.Where there are two chainwheels the lower arm pivot axis 20 ispreferably located at or below the horizon of the tangent point of thetension run 30 of the drive chain with the smaller of the two.

As is apparent from the Figures, the path of movement of the upper endsof upper arm members 3, 103, which are rigidly attached to the lower endof shock absorber 5, is constrained by the telescoping of the shockabsorber and by the pivotal movement of the upper element of the shockabsorber as the lower arm elements move upward and downward in responseto riding surface irregularities or applications of surges of power tothe rear sprocket through the drive chain. And the extent of themovement of the upper ends of upper arm members 3, 103 is limited by thestrength of resiliency of the shock absorber.

According to the invention, as the lower arm members flex upward anddownward in response to irregularities in the riding surface, or assurges of power are applied to the rear sprocket through the chain, therear wheel axle moves not in a simple vertical arc centered at the lowerarm pivot axis; rather, the rear wheel axle "floats" in a directiongenerally upward and slightly more rearwardly, as determined by thecombination of the pivoting movements of the lower and upper arms andthe shortening and lengthening of the distance between the rear pivotaxis 4 and the upper pivot point 6 as the shock absorber 5 respondsresiliently to the upward force component at the rear hub. As a result,the movements of the suspension are effectively isolated to some degreefrom the pedal forces, reducing jacking and improving the performance ofthe bicycle.

An alternative and still more preferred embodiment is shown in FIGS. 3and 4, in which corresponding parts are identified by correspondingreference numerals. In this embodiment, the upper arm members 3, 103 andthe lower arm members 2, 102 and the seat tube 14 are linkedsubstantially as in the embodiment shown in FIGS. 1 and 2, and describedabove; and the positions of the lower arm pivot axis 20 in relation tothe crank axis 28 and the chainwheel, and of the rear pivot point 4 inrelation to the rear hub axis 26, are substantially as described.

In the embodiment of FIGS. 3 and 4, lever 11 is provided to pivotallylink the upper ends of upper arm members 3, 103 to the main frame. Theupper ends of upper arm members 3, 103 are pivotally attached to one endof lever 11 at pivot point 9, and the other end of lever 11 is pivotallyattached to seat tube 14 at pivot point 8. A shock absorber 10 isoperationally attached about a point 40 intermediate to the ends of thelever and a point 42 above the pivot point 8 on seat tube 14. It can bepreferable to provide for pivotal attachment of shock absorber 10 to thelever at 40 or to the seat tube at 42, or at both points 40 and 42.

In this embodiment, the path of movement of the upper ends of upper armmembers 3, 103 is thus constrained to an arc having its center at pivotpoint 8 and having a radius equal to the distance between pivot points 9and 8. And the extent of the movement of the upper ends of upper armmembers 3, 103 is limited by the resiliency of the shock absorber.

As will be appreciated, certain of the members of the suspensiondescribed above are paired so that they accommodate and embrace the rearwheel. In fact, of course, each set of paired right and left members isintended to pivot together as a unit, and corresponding members of eachpair are rigidly Joined to one another by methods known in the bicycleart. Unitary movement of the rigidly joined pairs about the respectivepivot points ensures that the rear wheel hub axis, the crank axis, andall the pivot axes remain substantially parallel to one anotherthroughout the range of movement under the stresses of the ride.Selected portions of the paired members can be fully united at least ata pivot point. For example, the lower arm members may be fully unitedtoward their front ends; the upper arm members may be fully united attheir upper ends; and the lever (in the embodiment shown in FIGS. 3 and4) need not be a paired structure at all, except as may be convenientfor making a stable and sturdy pivoting connection with the seat tubeand the upper arm members, and as may be convenient for mounting shockabsorber 5; an A-arm configuration may be preferred.

In preferred embodiments, caliper brakes are used, and the rear calipercan be mounted on one or both of upper arm members (or on a bracejoining the pair near their upper ends) adjacent the rim of the rearwheel. Application of the brake has less effect on the suspensionresponse when the caliper is mounted on the upper arm member in theconfiguration according to the invention than when the caliper ismounted on the swing arm, as is conventional. Also, in preferredembodiments, the rear derailleur can be mounted on an upper arm member.

vi. INDUSTRIAL APPLICABILITY

The rear suspension according to the invention provides for improvedsafety and performance, by effectively to some extent isolatingmovements of the suspension from pedal forces. As a result, the rearwheel is kept for a greater proportion of the riding time in goodcontact with the riding surface, even when the rider applies bursts ofpower to the rear wheel through the chain, and even where the ridingsurface is exceedingly irregular. The suspension can therefore be usedwith salutary effect particularly on so-called "mountain bikes" or"trail bikes" where high performance is demanded, as in competitiveoff-track riding. The invention provides for lightweight straightforwardconstruction, and can be adapted to any of a variety of standardconventional main frames, so it is suitable for retrofit.

OTHER EMBODIMENTS

Other embodiments are within the following claims.

I claim:
 1. A bicycle frame comprising:a main frame including a toptube, a down tube, and a seat tube, including a bottom bracket embracinga crank axis near the main frame lower apex, said crank axis defining anaxis for rotation; a plurality of chainwheels of differing diametersmounted on said bottom bracket embracing said crank axis; paired rightand left lower arm members each having a front end and a rear end, saidfront ends of said lower arm members being pivotably connected to themain frame such that said lower arm members are pivotable about a lowerarm pivot axis located above said crank axis; paired right and leftupper arm members each having an upper and a lower end, said lower endof each upper arm member being pivotally connected to a respective oneof said lower arm members, such that said upper and lower arm membersare pivotable about a rear pivot axis near said rear ends of said lowerarm members, said upper arm members defining a location for receiving arear wheel axle having an axis such that said location is spaced above aline connecting said lower arm pivot axis and said rear pivot axis; aplurality of sprockets of differing diameters mounted on said rear wheelaxle; a resistance assembly, comprising:a lever unit having a first endand a second end, said lever unit pivotally connected at said first endto the main frame and pivotally connected at said second end to saidupper end of said paired fight and left upper arm members; and a shockabsorber pivotably connected to said lever unit between said first endand said second end, said resistance assembly substantially continuouslyproviding effectively all resilient resistance to movement of said upperends of said upper arm members.
 2. The bicycle frame of claim 1, whereinsaid lever comprises an A-arm.
 3. The bicycle frame of claim 1, whereinsaid shock absorber comprises a spring.
 4. The bicycle frame of claim 1,wherein said shock absorber comprises an elastomer.
 5. The bicycle frameof claim 1, wherein said shock absorber comprises a spring and elastomerin combination.
 6. The bicycle frame of claim 1, wherein said shockabsorber comprises a hydraulic shock absorber.
 7. The bicycle frame ofclaim 1, wherein said shock absorber comprises a spring and hydraulicshock absorber in combination.
 8. A bicycle frame comprising:a mainframe including a top tube, a down tube, and a seat tube, including abottom bracket embracing a crank axis near the main frame lower apex,said crank axis defining an axis for rotation; a plurality ofchainwheels of differing diameters mounted on said bottom bracketembracing said crank axis; paired right and left lower arm members eachhaving a front end and a rear end, said front ends of said lower armmembers being pivotably connected to the main frame such that said lowerarm members are pivotable about a lower arm pivot axis located abovesaid crank axis; paired right and left upper arm members each having anupper and a lower end, said lower end of each upper arm member beingpivotally connected to a respective one of said lower arm members, suchthat said upper and lower arm members are pivotable about a rear pivotaxis near said rear ends of said lower arm members, said upper armmembers defining a location for receiving a rear wheel axle having anaxis such that said location is spaced above a line connecting saidlower arm pivot axis and said rear pivot axis and is spaced above thehorizon of said rear pivot axis; a plurality of sprockets of differingdiameters mounted on said rear wheel axle; a resistance assembly,comprising:a lever unit having a first end and a second end, said leverunit pivotally connected at said first end to the main frame andpivotally connected at said second end to said upper end or said pairedright and left upper arm members; and a shock absorber pivotablyconnected to said lever unit between said first end and said second end,said resistance assembly substantially continuously providingeffectively all resilient resistance to movement of said upper ends ofsaid upper arm members.
 9. The bicycle frame of claim 8, wherein saidlever comprises an A-arm.
 10. The bicycle frame of claim 8, wherein saidshock absorber comprises a spring.
 11. The bicycle frame of claim 8,wherein said shock absorber comprises an elastomer.
 12. The bicycleframe of claim 8, wherein said shock absorber comprises a spring andelastomer in combination.
 13. The bicycle frame of claim 8, wherein saidshock absorber comprises a hydraulic shock absorber.
 14. The bicycleframe of claim 8, wherein said shock absorber comprises a spring andhydraulic shock absorber in combination.